Measuring IRTF image quality and modeled improvement through use of FELIX and the prototype adaptive secondary mirror

Image quality on the NASA Infrared Telescope Facility (IRTF) is currently limited by telescope-induced aberrations when seeing is good. We have measured telescope image quality as a function of telescope pointing over several recent epochs to quantify these aberrations. Using the measured aberrations and seeing, we “Donut” modeled the expected image quality improvements through applications of the soon-to-be commissioned off-axis Shack-Hartmann (S-H) wavefront sensor and CCD camera, FELIX. The average telescope-induced wavefront error without defocus is 0.7 ± 0.04μm RMS, the largest contributor being astigmatism (∼0.21μm RMS). Uncorrected images would require ∼ 2 times longer integration times to compensate for light loss through seeing-limited slits. Our models indicate that active control of the hexapod-mounted secondary mirror by a 2x2 S-H in FELIX can accurately correct the largest current aberration (defocus). However, a 3x3 S-H is needed to correct higher-order telescope aberrations using the proposed Adaptive Secondary Mirror (ASM).